For example, in an automatic photographic printing operation, a continuous strip of photographic paper is intermittently fed to a printing position, and it is necessary in order to carry out proper printing to accurately feed the photographic paper along a predetermined guide path.
Photographic paper varies in width, therefore, it is necessary to change the width of the photographic paper guide path accurately so as to conform to the width of the photographic paper being used.
A typical conventional means for changeably setting the width of a sheet guide path has a shaft that crosses the guide path and a pair of sheet guide members which are mounted on the shaft at both sides, respectively, of the guide path to define the width of the guide path, the guide members being in engagement with respective threads which are provided on both end portions of the shaft in opposite directions to each other, so that the guide members move toward and away from each other on the shaft in response to the rotation of the shaft, thereby determining the respective portions of the guide members, and thus setting the width of the guide path.
The above-described conventional apparatus for changeably setting the width of the guide path suffers, however, from the following disadvantages:
It is difficult to rotate the shaft accurately, and since undesirable play, for example, backlash in the thread engagement, is likely to occur, it is difficult to position the guide members accurately by rotation of the shaft. In order to overcome these disadvantages, a sensor of high accuracy and a complicated detecting mechanism are needed.